Electron collector for travelling wave tubes and the like



Oct. 20, 1964 P. MEYERER 3,

ELECTRON COLLECTOR FOR TRAVELLING WAVE TUBES AND THE LIKE Filed June 14, 1961 United States Patent 3,153,743 ELECTRON COLLECTOR FOR TRAVELLING WAVE TUBES AND THE LEKE Paul Meyerer, Munich, Germany, assignor to Siemens &

Halske Aktiengesellschaft Berlin and Munich, a corporation of Germany Filed June 14, 1961, Ser. No. 117,076 Claims priority, application Germany Sept. 20, 1%0 19 Claims. (Cl. 315-538) This invention is concerned with an electron collector for travelling wave tubes and the like, comprising means forming a hollow space for receiving the electron beam, and a diaphragm for closing said beam-receiving space toward the discharge space of the tube.

Among the requirements posed for an electron collector for travelling wave tubes, return waves oscillators, klystrons, and the like, is the requirement that the collector must absorb and radiate to the outside the heat produced by the loss factor of the electron beam. Attempts at meeting this requirement are made diflicult because constructional reasons usually stand in the way of making the diameter and the length of the collector as large as desired. The collector must also be constructed so that the secondary electrons released responsive to the impact of the electron beam on the wall of the collector, cannot reach the discharge space.

Previously known collectors usually consist of a metal part forming an elongated tubular hollow space into which the electron beam enters after passing through the discharge space. This hollow space is free of e ectric and magnetic fields. Owing to its space charge, the elec tron beam diverges within the hollow space, so that the electrons are uniformly distributed over the inner wall of the collector. The hollow space is by means of a diaphragm closed toward the discharge space in order to prevent reentry of secondary electrons into the latter. The direct voltage on the trap is usually lower than the voltage lying on the system parts of the amplifier portion of the tube, for example, on the delay line, so as to decrease losses at the trap.

In case of the above described known collectors, the hollow space must be relatively long so as to obtain a sufficiently great divergence of the electron beam, thereby avoiding going beyond the permissible loading of the collector wall by the electron impact. High capacity travelling wave tubes or high capacity klystrons require a length of the collector which reaches the limit of constructional possibilities. It was moreover found that it is impossible, despite the diaphragm which delimits the hollow space and despite the great length of the hollow space, to prevent exit from the collector of the fast secondary electrons which are released at the base thereof. The problem concerning the secondary electrons is particularly critical in the case of collectors which are, for the reduction of the loss effect, provided with a lower direct potential than, for example, the delay line, since the secondary electrons leaving the collector are accelerated.

In order to overcome the above indicated difiiculties, it is in accordance with the invention proposed to provide in connection with a collector for travelling wave tubes and the like, within the hollow space which receives the electron beam and which is by means of a diaphragm closed toward the discharge space, a magnetic field with a field line course which is directed so as to extend radially with respect to the axis of the electron beam.

In a collector according to the invention, and as a consequence of the presence, within the hollow space, of the magnetic field which is oriented radially with respect to the electron radiation axis, there is imparted to the electrons of the electron beam a rotary motion operating in 3,153,743 Patented Oct. 20, 1964 addition to the motion thereof in the radiation direction. A Lorentz force directed radially with respect to the radiation axis can not be produced thereby and the electrons are accordingly driven radially outwardly owing to the centrifugal force which becomes operative as a result of the rotary motion thereof. It is therefore possible, depending upon the magnitude of the radial field strength, to increase the diameter of the electron beam over a relatively short path as rapidly as desired. The magnetic field is moreover operative with respect to the secondary electrons which are released at the side wall of the hollow space, affecting the secondary electrons so that they practically cannot leave the collector wall. The fast secondary electrons which are released at the base of the collector are deflected by the magnetic field so that they impact the diaphragm which terminates the hollow space or the side wall thereof. An emission of secondary elec trons into the discharge space of the tube is thus entirely prevented.

The various objects and features of the invention will now be explained with reference to the accompanying drawing showing embodiments thereof. Parts which are not necessary for an understanding of the invention have been omitted in the drawing. Corresponding parts are identically referenced.

FIG. 1 shows part of a travelling wave tube at the collector end thereof which is constructed in accordance with the invention;

FIG. 2 is a sectional view taken along line A-B of FIG. 1, indicating the magnetic field course;

FIG. 3 represents an embodiment of a collector for tubes of average capacity, requiring only relatively slight divergence of the electron beams; and

FIG. 4 shows a collector comprising in accordance with the invention a metal tube made of ferromagnetic material.

The pot-shaped collector 1 shown in FIG. 1 is by means of an intermediate tubular glass member 2 fused to a disk-shaped metal ring 3 which is made, for example, of Kovar. This metal ring 3 terminates the discharge vessel 4 which delimits the discharge space and serves for holding the delay line 5. An electron beam 6 which is within the delay line 5 guided in bunched manner throughout the length of the discharge space, reaches the interior of the collector 1 through the opening of the metal ring 3 and through the aperature of the diaphragm 7 which closes the pot-shaped collector toward the discharge space. Outside of the collector 1 are disposed in star formation a plurality, for example, four rod shaped permanent magnets 8, the magnetic axes of which are, as shown in FIG. 2, oriented radially with respect to the radiation axis, the arrangement being such that all poles positioned adjacent to the collector, are of the same polarity. These magnets produce Within the collector 1, which is made of non-magnetic material, a magnetic field course such as indicated by arrows 9 in FIG. 2. This magnetic field, which could of course be also produced by means of a radially magnetized ring magnet surrounding the trap 1 coaxially, imparts to the electrons within the collector a rotational motion, thereby deflecting the electrons radially outwardly and producing a radiation course such as indicated in FIG. 1. It is in connection with this embodiment of particular advantage to provide getter material upon the base of the collector which is now practically free of electron impact.

It is in some cases of tubes of average capacity often sufficient to provide for relatively slight widening or divergence of the electron beam diameter within the hollow space of the collector. A collector according to FIG. 3 is for such tubes particularly suitable. The base of this collector, which is likewise pot-shaped, is made of non-magnetic material and the side wall 11 as Well as diaphragm which terminates the collector with respect to the discharge space, are made of magnetic material. At least two rod-shaped magnets 12 are disposed outside of the base of the collector. A ring magnet with radial magnetization may of course be used in place of the magnets 12. The poles disposed adjacent to the radiation axis are of the same polarity, resulting in a magnetic course as indicated by the arrows 13, which produces the indicated divergence or widening of the electron beam 6.

FIG. 4 illustrates a collector structure comprising a metal bushing 14 made of ferromagnetic material, in which is disposed, at the end thereof facing away from the discharge space, a ring magnet 15 with radial magnetization. A cone shaped member 16 projecting into the hollow space of the collector forms the magnetic counter pole with respect to the metallic bushing 14. The resulting magnetic field line course indicated by the arrows 17 produces again a widening of the electron beam 6. The metal bushing 14 is surrounded by a copper tubing 18 which may be provided with fins or the like, so as to facilitate the radiation of the heat produced at the collector. The ring magnet 15 is protected against electron impact by a copper ring 19 disposed upon the conical member 16.

The invention is not inherently limited to the examples illustrated in the drawing as it may be advantageously used in connection with other travelling wave tubes and the like, operating with a bunched or focused electron beam. It is merely important that there is within the hollow electron beam-receiving space of the collector a magnetic field with a substantially purely radially oriented field line course.

Changes and modifications may accordingly be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. An electron collector for a travelling wave tube and the like, comprising means forming a pot-shaped collector having a hollow space which receives the electron radia-' tion beam and having a diaphragm for closing such beam receiving space toward the discharge space of the tube, magnetic field-producing means disposed eXteriorly of but adjacent to said collector and forming opposite magnetic poles which are radially spaced and symmetrically disposed relative to the electron radiation axis, forming a magnetic field within the hollow space which has a field line course which is oriented radially to all sides and thereby free of a magnetic field having a field line course oriented parallel to the electron radiation axis whereby a rotary motion is imparted to the electrons of the radiation beam, with the resulting centrifugal force thereon being operative to produce a rapid divergence of said beam within the collector.

2. An arrangement according to claim 1, wherein said collector comprises a pot-shaped body made of non-magnetic material and forming said hollow space, and permanent magnet means for producing said magnetic field disposed outside of said body adjacent the side walls thereof.

3. An arrangement according to claim 1, wherein said collector comprises a pot-shaped body made of non-magnetic material and forming said hollow space, and four permanent magnets arranged in star-formation outside about the outside wall of said body.

4. An arrangement according to claim 1, wherein said collector comprises a pot-shaped body made of non-magnetic material and forming said hollow space, four permanent magnets arranged in star-formation outside about the outside wall of said body, and getter material disposed upon the inner wall of the base of said hollow space.

5. An arrangement according to claim 1, wherein said collector comprises a body having a side wall and a base wall forming said hollow space, said side wall being made of magnetic material and said base wall being made of non-magnetic material, and radially oriented magnet means disposed adjacent said base wall outside thereof.

6. An arrangement according to claim 5, wherein said magnet means is a radially magnetized ring magnet.

7. An arrangement according to claim 5, wherein said magnet means comprises at least two rod-shaped magnets with radially oriented magnetic axes.

8. An arrangement according to claim 1, wherein said collector comprises a metal bushing made of ferromagnetic material, said metal bushing containing, at the end thereof which faces away from the discharge space, a radially magnetized ring magnet inserted therein coaxially with the electron beam axis, and a cone shaped member projecting from said magnet inwardly into said hollow space.

9. An arrangement according to claim 8, comprising a copper sleeve surrounding at least the part of said metal bushing which is subjected to electron impact, and a copper ring carried by said cone shaped member and engaging said ring magnet.

10. An arrangement according to claim 1, comprising an intermediate tubular glass sleeve fused at one end to a metal disk which terminates the discharge vessel of the tube and fused at the other end to said collector for bolding such collector in assigned position with respect to said vessel.

References Cited in the file of this patent UNITED STATES PATENTS 2,220,556 Thorson Nov. 5, 1940 2,853,641 Webber Sept. 23, 1958 2,955,225 Sterzer Oct. 4, 1960 3,012,170 Heil Dec. 5, 1961 3,067,347 Rose Dec. 4, 1962 

1. AN ELECTRON COLLECTOR FOR A TRAVELLING WAVE TUBE AND THE LIKE, COMPRISING MEANS FORMING A POT-SHAPED COLLECTOR HAVING A HOLLOW SPACE WHICH RECEIVES THE ELECTRON RADIATION BEAM AND HAVING A DIAPHRAGM FOR CLOSING SUCH BEAM RECEIVING SPACE TOWARD THE DISCHARGE SPACE OF THE TUBE, MAGNETIC FIELD-PRODUCING MEANS DISPOSED EXTERIORLY OF BUT ADJACENT TO SAID COLLECTOR AND FORMING OPPOSITE MAGNETIC POLES WHICH ARE RADIALLY SPACED AND SYMMETRICALLY DISPOSED RELATIVE TO THE ELECTRON RADIATION AXIS, FORMING A MAGNETIC FIELD WITHIN THE HOLLOW SPACE WHICH HAS A FIELD LINE COURSE WHICH IS ORIENTED RADIALLY TO ALL SIDES AND THEREBY FREE OF A MAGNETIC FIELD HAVING A FIELD LINE COURSE ORIENTED PARALLEL TO THE ELECTRON RADIATION AXIS WHEREBY A ROTARY MOTION IS IMPARTED TO THE ELECTRONS OF THE RADIATION BEAM, WITH THE RESULTING CENTRIFUGAL FORCE THEREON BEING OPERATIVE TO PRODUCE A RAPID DIVERGENCE OF SAID BEAM WITHIN THE COLLECTOR. 